Vincristine and Temozolomide in Combination With PEN-866 for Adolescents and Young Adults With Relapsed or Refractory Solid Tumors

Background: The drug PEN-866 can remain in tumor cells longer than it does in normal cells. It also may be more effective than other drugs at treating Ewing sarcoma and rhabdomyosarcoma. Researchers want to learn if combining PEN-866 with other drugs can treat certain cancers in adolescents and young adults. Objective: To learn if the combination of PEN-866 with vincristine and temozolomide can be used to treat adolescents and young adults with solid tumors that have returned after or did not respond to standard treatments, or for which there are no standard treatments. Eligibility: People ages 12-39 years who have solid tumors, Ewing sarcoma, or rhabdomyosarcoma that returned after or did not respond to standard treatments. Design: Participants will be screened with a medical history, physical exam, and eye exam. They will have heart function tests. They may have imaging scans of the chest, abdomen, and pelvis. They will give blood and urine samples. They may have a tumor biopsy. Some samples will be used for genetic testing. Some screening tests will be repeated during the study. Participants will get 3 drugs for up to 18 cycles. Each cycle lasts 21 days. They will get PEN-866 and vincristine by IV infusion (a tube in their vein) on Days 1 and 8 of each cycle. They will take temozolomide by mouth on Days 1-5 of each cycle. Participants will complete questionnaires about their physical, mental, and social health. Participants will have a follow-up visit 30 days after treatment ends. They may be contacted by phone or email for the rest of their life.